Continuous wave (CVV) and pulsed infrared lasers, producing radiation within the wavelength range of approximately 1.5 μm to 2.2 μm, are useful for minimally invasive ablation/vaporization of soft tissues. Functionally, this utility is due to the high water content of tissue strongly absorbing infrared radiation in this range; commercially, this utility is due to the availability of relatively low cost, flexible, reliable and biocompatible silica core optical fiber for delivery of these wavelengths. Concentrated and localized heat is produced at the tissue and imposes an upper limit on the average power that may safely be applied without severely damaging the delivery device; even at moderate-average power this heat damages lateral delivery surgical fibers.
Coaxial cooling, where water flows about the fiber circumference at the output, has been used to extend the lifetime and upper power limit of lateral delivery devices, but strong absorption in the near infrared limits the utility of these devices outside shorter wavelengths, e.g., those within the biological window. At longer wavelengths (e.g., 1.5 μm to 2.2 μm), a ‘Moses bubble’ (a steam bubble) is generated whenever sufficient laser energy encounters water (or aqueous solutions like sterile urological irrigation fluids). When pulsed lasers are used, such as holmium lasers, a distinct popping sound is produced as a steam bubble forms and collapses with each laser pulse. A constant stream of steam bubbles displaces the cooling water in water-cooled side fire fibers leading to thermal damage and the practical exclusion of these fibers at wavelengths in the range where water absorbs strongly.
Generally, gravity-fed (low pressure) coaxial cooling of a side fire fiber greatly improves the fiber useful lifetime (FIG. 6). Prior to these designs, the best side fire fibers on the market survived between 100,000 joules and 250,000 joules before becoming so devitrified and pitted that the output direction and the output spot irradiance became unsafe and ineffective. Damage to the fibers include water intruding into the protective cap via a through-wall perforation (indicated by axial emission), and the cap detaching from the fiber or the fiber simply melting away. Prior to these designs, approximately 15% of all 532 nm laser prostate resection cases required a second fiber to complete surgery and some cases required three fibers (e.g., Laserscope/AMS fiber model 2090 fiber, 80 W or 120 W @ 532 nm). The water-cooled design typically survives 650,000 joules without catastrophic damage even while the 532 nm laser output power has been increased to 180 W.
Variations abound in fiber device tips for surgical applications and the following are directed, primarily, at the side firing devices. This list shows examples that incorporate some aspect of cooling, or potential cooling, of the side fire fiber or tip.
U.S. Pat. No. 5,246,436 (Rowe) describes a fiber device with a metallic and reflective coating on the tip of a conically polished fiber and a void (a hole or port) in the reflective coating permitting light to exit. The tip of the fiber is surrounded by a water channel where the fluidic exit corresponds to the light exit. Rowe teaches (Moses) bubble formation beginning within the emission optical path and within 5 microseconds post laser pulse initiation, followed by bubble expansion with a second laser pulse such that the subsequent pulses pass through the steam bubble to the target tissue.
U.S. Pat. No. 5,409,483 (Campbell, et al.) teaches a side firing fiber device complete with direct visualization of the proximate area about a side fire fiber with the fiber centered in a saline filled balloon. Campbell teaches saline pressure inflating the balloon to compress the targeted tissue to permit deeper penetration of coagulating energy density.
U.S. Pat. No. 5,454,807 (Lennox, et al.) teaches the provision of coaxial coolant flow, gaseous or liquid, for prevention of surface tissue damage for the stated reason of permitting the application of more laser energy to underlying tissues for exogenous chromophore activation in photodynamic therapy (PDT).
U.S. Pat. No. 5,496,309 (Saadat, et al.) discloses fluid flow about a light redirecting prism (that is in communication with the flat tip of an optical fiber) where the prism TIR surface is in contact with the fluid. As such, the prism must be composed of a non-silica material with a refractive index significantly higher than that of the fluid in order to support right angle redirection under the constraints of Snell's law. Fluid flow and laser energy exit a common port.
U.S. Pat. No. 5,672,171 (Andrus, et al.) teaches an axial emitting fiber, housed within a cannula through which saline is flowed to maintain the fiber temperature under approximately 100° C. during use, delivering up to 10 W of 1064 nm (Nd:YAG laser) energy.
U.S. Pat. No. 5,685,824 (Takei) teaches a “prostascope” provisioned with a standard working channel to accept an optical fiber and deliver irrigant to the general surgical field (as does any standard cystoscope) but where a reflector is positioned within a side opening of the working channel for redirecting laser energy laterally with respect to the scope longitudinal axis.
U.S. Pat. No. 6,802,838 (Loeb, et al.) teaches a side firing fiber housed within a nested, dual coaxial lumen device whereby cooling fluid is passed about the side fire fiber within the central lumen, with light exiting a common port with the fluid, and where coolant fluid and debris are evacuated through the second, surrounding lumen.
U.S. Pat. No. 6,953,458 (Loeb) teaches a coaxial coolant channel about an axial fiber where a gas and laser energy exit a common port, where the channel may be angled for access to orthogonally situated tissues, where the gas produces a substantially fluid-free optical path for the laser radiation to reach target tissues.
U.S. Pat. No. 7,359,601 (Loeb) is a continuation-in-part of Loeb '458, teaching adaptations for standard side-firing fibers and teaching suitability of bare, bevel-tipped side fire fibers, operating in irrigation fluid-free space provided by the gas flow.
U.S. Pat. No. 7,492,987 (Yeik, et al.) teaches avoidance of “erosion” of side fire fiber caps that is said to be due to both scatter (or stray or aberrant emissions) laser energy and “back-scattered” laser energy from the tissue itself, with degradation of performance (or loss of laser energy delivery efficiency) from damage to the TIR beveled tip of the optical fiber or capillary in which an optical fiber with the “distal end beveled at an angle of about 30° to 50° is encased in a closed-ended capillary tube for internal reflection of the laser energy, using laser energy of wavelengths of about 300 to 3000 nm”. Improved device longevity is taught for fibers that are very similar to those taught by '601, but with the addition of a reflective metal strip or coating within the bore of a needle-like sheathe that acts to form a fluid channel about the glass capsule. An increase in contact vaporization longevity from 86,206 J (3.07 J per pulse, 26 pps, and 18 minutes to failure) to greater than 287,352 J (same settings, one hour and still functioning) is taught to be a result of the addition of a silver metal strip behind and around the glass capsule.
U.S. Pat. No. 7,909,817 (Griffin, et al.) discloses a dual cap side fire fiber where the side fire function is provided within the inner, thin walled cap, and the protective function is performed by a thicker, outer cap, with cooling provided by irrigation fluid flow in the annular space that is formed between the two caps. This technology will not function in the infrared region of interest herein, due to ‘Moses bubble’ formation within the confined space interfering with coolant fluid flow, but at the 532 nm of the GreenLight XPS™ laser, it is the most widely used side fire fiber to date: American Medical Systems' MoXy™ fiber (AMS is currently a part of Boston Scientific and owns the preceding trademarks).
U.S. Pat. No. 8,529,561 (Griffin, et al.) is a divisional of Griffin '817 describing methods for disruption of laminar flow within the annular, coaxial fluidic conduit.
U.S. Pat. Pub. No. 2014/0074072 (Griffin, et al.) is a continuation-in-part of Griffin '561, teaching rotation of the outer, secondary capsule during surgery.
U.S. Pat. No. 8,858,542 (Peng, et al.) describes a side fire fiber that is cooled within and around the fiber output, with coolant flow exiting a common port with laser radiation and coaxially about the fiber tip.
U.S. Pat. Nos. 8,932,289, 9,005,195 and 9,017,324 (Mayse, et al.) teach cryogenically cooled tissue ablation devices for treatment of chronic obstructive pulmonary disease with various forms of energy, preferably radio frequency energy (but including laser energy) where cryogenic coolant is delivered via a lumen to a balloon, within which or about which resides the energy delivery electrode or presumably an optical fiber or fibers (in the case of ablation by laser energy).
Another tactic for improving the life expectancy of surgical fibers includes coaxial cooling of fiber tips with gas flow. As early as the 1980s, “gas-cooled” Nd:YAG laser compatible fibers were produced for ‘open surgery’ applications (often non-endoscopic and with no irrigation) such as found in the ear, nose and throat (ENT) specialization, where a circumferential sheathe of gas protects fiber output tips, from accumulation of blood and tissue ejecta. A niche market remains for these fibers even today.
Other rationalizations for passing gases and liquids across fiber surfaces or over tissues appear in the prior art, e.g. cooling tissue in cosmetic and other non-ablative laser procedures to permit more laser interaction with target chromophores before reaching pain or damage thresholds (tattoo ink, spider veins, port wine stains and activation drugs for PDT), where the coolant is provided coaxially to the target (as opposed to the fiber), e.g. U.S. Pat. No. 6,436,094 (Reuter). In endosurgical applications of lasers, much of the cooled fiber prior art is concerned with side firing fibers for laser vaporization of the prostate or axial firing fibers for prostate enucleation.
Relying upon delivered gas to bubble past the irrigation flow within the cystoscope working channel is likely inadequate for providing sufficient gas to displace the irrigant while simultaneously providing adequate irrigation. Surgical interventions can take more than an hour: e.g. for relief of the symptoms of benign prostatic hyperplasia (BPH) where the surgical site is the prostatic urethra, adjacent to the urinary bladder. Were pressures within the urethra to rise sufficient to open the interior sphincter, inflating the bladder, the ureters and ultimately the kidneys, potentially fatal consequences could result due to gas perfusion into the extensive kidney capillary bed. Perfusion into capillaries exposed by the surgery itself could be problematic on its own. While some portion of the optical path may be free of water during some portion of energy delivery events at sheath gas flows compatible with BPH surgery, total displacement of irrigant from the optical path is improbable, and were it possible, the fiber tip would rapidly overheat and melt under modern surgical conditions. In fact, all known commercially available side fire fibers instructions for use caution against firing in air. In-house testing of market available holmium laser compatible side fire fibers demonstrated that the fibers are catastrophically damaged at 20 watts, average power.